The present invention relates to a sterile water collector of the type comprising a sampling device and a sample receptacle arranged to be activated by external actuation, whereby an inlet to the evacuated sample receptacle is opened.
Sampling of water for bacteriological tests necessiates that the samples can be collected without being contaminated by foreign bacteria. Such sampling is used e.g. at bacteriological control of bathing and drinking water or for determination of the number and activity of bacteria in different water systems. Different water collectors have been designed for such purposes, but none of those conventional water collectors fulfil all requirements which are made of a practically manageable, sterile water collector. Those requirements are:
Sampling device and sample receptacle shall be separable units. It is desirable for economic reasons that several sample receptacles can be used on the same sampling device, as the sampling device for a sterile water collector requires some technical contrivances. The manageability of the sample increases further if the sample receptacle can be separated from the sampling device when recovered from the water.
The water collector shall be usable together with a wire from a winch as well as with a separate rope. A wire from a ship is commonly used, but sampling from jettys, in wells and the like necessiates that the collector can be used on a single rope.
Fitting and maneuvering of the water collector shall be realizable with simple hand grips. Such factors as rough seas, coldness and the use of clumsy gloves must not hamper the sampling work.
The sample shall be collected so far from the collector that there is no risk for contamination from the wire and sampling device. This is a requirement, as bacteria may accompany the collector and wire down through the water and then contaminate the sample, and these bacteria are not representative for the water at the sampling level if the sample is collected immediately adjacent the collector or wire.
It shall be possible to use several collectors on the same wire simultaneously, as samples are often desired from several levels at the same time. When the collector is activated by means of a plummet which runs along the wire, a second plummet is to start from a level below or above the collector just activated in order to activate the next collector etc.
The inlet for sample water shall be open only during the time for collecting the sample. If the inlet is open during the entire time of submersion or recovery the risk for contamination is of course increased.
Sampling device and receptacle shall be able to operate without problems on large depths at high pressures.
It shall be possible to sterilize the sample receptacle, preferably by means of an autoclave, which can easily be accomplished at sea.
The sample receptacle shall be a cheap disposable article or it shall be reusable after machine dish-washing.
The water collector shall be manufacturable for sample volumes between about 0.3 liters and 10 liters without the function being altered.
Sampling device and receptacle must withstand rough treatment.
For certain tests it must be possible to make the sample receptacle impermeable to light.
The collector shall withstand low temperatures. The temperature of the surface water of the sea can, during the winter, be about -3.degree. C. and the air temperature can be considerably lower. The collector should not become brittle at such temperatures.
Earlier sterile water collectors use as activating member a plummit, which is dropped along the carrying wire and which when reaching the collector by means of its kinetic energy starts the sampling.
One of these older water collectors is the ZoBell collector, which operates with a sterile and evacuated glass bottle to which is connected a rubber tube, which at one of its ends is closed by means of a glass tube. When the plummit is dropped and hits the glass tube this is broken and the rubber tube is, by means of its inherent flexibility, swung out from the sample receptacle. Water flows into the bottle and fills it. At the same time a second plummit is activated and dropped from the activated collector and is allowed to sink to the next collector etc. Advantages of this ZoBell collector are that it is easy to handle and that it collects the sample some distance away from the collector. Its drawbacks are that it can not operate on depths larger than 50-100 meters, and that the sample receptacle is open after activation.
The water collector most frequently used in microbiology is the Niskin-collector, in which a falling plummit releases a knife, which cuts a hole in a sterile plastic bag threaded over the spring-loaded wings of the collector. A rubber tube for collecting the sample then swings out a short distance from the collector, at the same time as the spring force causes the wings to be filled out, whereby the bag is filled. The bag is thereupon automatically closed by a closing mechanism. This collector has the advantages that it is closed immediately after the sampling, it can be used at great depths and large volumes can be collected. Its drawbacks are that use of the collector requires several careful hand grips made simultaneously which is time-wasting and difficult. The plastic bag is furthermore disposable and the cost for each bag is high, about 10 to 15 Swedish Krona, and at the same time as the bag is frail whereby it can easily leak at handling. Furthermore the knife which cuts off the plastic bag can contaminate the contents, and finally bigger collectors of this type are very difficult to handle.